Mind map

Chemistry

Kelly Powers English

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Chemistry

The structure of the Earth
- The inner core is mostly made of iron and nickel
  - Very dense and hot (5500 degrees)
- The outer core is mostly made of iron and nickel
  - Very hot and is also molten
- The mantle is mostly solid, with some liquid proerties
- The Earth's crust is a thin layer of rock at the surface upon which we live
  - Mostly made of sand Si02
Plate tectonics
- 12 plates
- Float on the semi-molten mantle
  - Convection currents within the mantle cause the plates to move
- They move about 2cm a year
- Convection currents
  - Rock near core is melted, becomes less dense and rises to the crust
    - This displaces more dense rock nearer the crust
Evidence for continental drift
- The jig saw fit
- Similarity in rock layers
- Similarities in the type and age of fossils
- Related species
Tectonic plates
- When tectonic plates move apart they create new rock
- When tectonic plates of equal density collide they cause mountains
- When the plates move sideways against each other they cause friction and stress builds up, causing earthquakes
- When two tectonic plates collide, the denser one subducts and forms a volcano over time
Thermal decomposition
- One product is broken down in the presence of heat to create more than one product
Concrete
- Made of small stones and aggregate, sharp sand, cement and water
- Strength under compression
- Weak under tension
- Reinforced concrete consists of steel bars set unto the concrete
Extracting metals from their ores
- Ore : Rock containing a metal or metal compound
- Malachite : Ore that contains copper carbonate
- Haematite : Ore that contains iron oxide
Reactivity series
Extracting Pure Copper
- Electolyte : Molten solution of compound
- Electrode : Metal or graphie rod that connects the electricity supply to the electolyte
- Anode : Positive
- Cathode : negative
- Purification of copper
  - The copper ions are attracted to the cathode where they gain 2 electrons and they turn to copper atoms which coat the cathode
    - Cu2+ (aq) + 2e- -> Cu (s)
    - The copper atoms loose electrons to form copper ions which then go into the solution. These ions are attracted to the cathode as before
      - Cu (s) - 2e- -> Cu2+ (aq)
Reasons to Cook
- Kills harmful microbes as it uses high temperatures
- Improves texture of the food
- Improves the taste and flavour of the food
- Makes the food easier to digest
Emulsifiers
- Emulsifiers are agents that cause substances to mix that would not ordinarily do so
- The substance formed is an emulsion
- Emulsifiers are agents that cause substances to mix that wouldn't originally do so. This is also used in mayonnaise. The emulsifier surrounds the oil droplets making the hydrophilic head stay in the water and the hydrophobic tail to push inside the oil. This causes it to break down inton oil droplets and mix with the water, which it originally didn't do.
- Why do cakes rise?
  - Baking powder (sodium hydrogen carbonate) breaks down on heating, producing carbon dioxide gas. The bubbles of gas cause the cakes to rise as they try to escape the mixture
  - 2NaHC03 -> H20 + 2CO2 + Na2O
    - 2NaHC03 = Baking Powder
    - H20 = Water
    - 2CO2 = Carbon Dioxide
    - Na2O = Sodium oxide
- Food additives
  - Added for flavour
  - Added for taste
  - Added for colour
  - Added to improve texture and the overall life
  - Additives are assigned an E - number
Esters
- Esters can be made by reacting an acid with an alcohol
- Water is the by - product that is formed in the reaction
- Organic Acid + Alcohol -> Ester + Water
- Naming the Ester
  - Ethanoic acid + methanol -> methylethanoate + water
- Perfume
  - Volatility - they vapourise quickly
    - Volatility of perfumes can be explained using the kinetic theory of particles
      - Particles iin a perfume are attracted to each other by weak intermolecular attractions
        It is easy to overcome these attractions so perfume particles seperate away from each other easily and the scent spreads quickly
  - Non toxic - they don't produce toxic vapours
  - Unreactive with water
  - Does not irritate the skin
  - Insoluble in water - so they don't wash off quickly
Paints and Pigments
- why use paint?
  - Protection - woodwork is painted to protect it from the rain
  - Decoration - we enjoy seeing a variety of colour to look attractive
- Different types of paint
  - Emulsion
    - These are water based paints typically consisting of water, pigment, polymer and extenders
  - Gloss
    - Gloss paint is an oil based paint. This means oil is the solvent for the pigment rather than the water. Ingredients are oil, pigment, solvent, extenders and additives
  - Oil
    - Oil paints used by artists contain similar substances to gloss. Oil pigment, solvent, extenders and additives
  - Thermochromic
    - Contains a pigment that changes colour as the temperature changes
    - Examples : mug/kettle which change colour because of heat/temperature change
  - Phosphorescent
    - Contains phosphorescent pigments that glow in the dark
    - These work by absorbing and storing light energy that they release over several hours
- How do paints work?
  - Paint is a mixture of solid particles that are mixed with liquid [articles but they are NOT dissolved. This is called a COLLOID. The pigment and binding medium particles are dispersed throughout the solvent particles. The solid particles are too small the separate and sink to the bottom. The solvent evapourates to leave a dry film of paint
  - All paints contain particles of coloured pigments, a solvent and a binding medium
    - PIGMENT - for colour
    - SOLVENT - thins the paint
    - BINDING MEDIUM - hardens the paint as it reacts with oxygen
Fuels
- What makes a good fuel?
  - Toxicity
  - Availability
  - Pollution
  - Cost
  - Energy values
  - Efficiency
- Formation of Crude Oil
  - Formed from the remains of animals in the sea that were buried under sand and rocks. Over millions of years, the heat and pressure, in the absence of air, converts the animal to oil. Gas is also produced
  - Trapped under rocks with heat and pressure but without air
  - Coal : formed from the remains of trees and plants on land that were buried under soil and rocks. Over millions of years, the heat and pressure in the absence of air, convert the plants and trees into oxygen
  - Fractional Distillation of Oil
    - Crude oil is a mixture of lots of different hydrocarbons. Hydrocarbons are chains of carbon atoms (e.g. alkanes and alkenes) of various lengths
    - The different compounds in crude oil are separated by fractional distillation. The oil is heated until most of it has turned into gas. The gases enter a fractionating column (and the liquid bitumen, is drained off at the bottom). In the column there's a temperature gradient, i.e. its hot at the bottom and it gets gradually cooler as you go up.
Clean air
- The Earth's atmosphere is a mixture of gases surrounding the planet. The Earth's gravity stops these gases escaping into space. The lower part of the atmosphere is the air that we breathe. It has stayed very much the same for the last 200 million years. The original atmosphere was formed by gases escaping from the Earth's interior : just two gases, nitrogen and oxygen make up about 99% of the air. Today, there are smaller proportions of other gases in the air, such as carbon dioxide, water vapour and noble gases such as argon
  - How is the early atmosphere thought to have been formed?
    - There was a lot of volcanic activity during its first billion years. When they erupt, volcanoes release huge volumes of gases. It is likely that the Earth's early atmosphere came from these volcanoes that released gases from inside the Earth's crust
      - Photosynthesis increased the levels of oxygen until it reached today's level
      - Photosynthesis reduced the levels of carbon dioxide in the atmosphere
  - Human influences on the composition of air
    - Deforestation
    - |ncreasing pollution
- Nitrogen = 78%
- Oxygen = 21%
- Carbon dioxide = 0.035%
- 3 main pollutants in the air
  - Carbon monoxide - poisonous
  - Oxides and nitrogen - Smog and acid rain
  - Sulfer dioxide - acid rain
Cracking
- The supply of some fractions may be greater than the demand for them. cracking is a chemical process that converts large hydrocarbon molecules into smaller, more useful hydrocarbon molecules. It involves heating oil fractions to a high temperature and passing them over a catalyst
- Cracking helps to match the supply of fractions to the demand for them, creating more of the widely used fractions such as petrol
- Octane and hexane are both alkanes, while ethane is an alkene. Alkenes are useful because they can be used to make polymers
- Alkanes
  - Hydrocarbons are compounds that contain only hydrogen atoms and carbon atoms. the alkanes are a family of hydrocarbons
  - General formula for alkanes
    - CnH2n+2
- Alkenes
  - The alkenes are another family of hydrocarbons. Unlike the alkanes, alkenes contain a double covalent bond between carbon atoms
  - Larger alkane hydrocarbons do not burn easily and are less useful. A process called CRACKING breaks large, less useful hydrocarbons into smaller, more useful hydrocarbons. A smaller alkane and an alkene are formed
    - Example : Cracking Octane
      - C8 H18 -> C5 H12 + C3 H6
        C8 H18 = Octane
        C3 H6 = Propene
        C5 H12 = Pentane
  - General formula for alkenes = CnH2n
Saturated or Unsturated
- Saturated means full. Alkanes are saturated hydrocarbons because there is no more space for any more atoms to add on
- Unsaturated means not full. Alkenes are unsaturated hydrocarbons because they contain double bonds where more atoms can add on across the double bond
Test for an alkene
- The test for an alkene is to use bromine water. There is no reaction between an alane and bromine water, the bromine water stayed yellow/orange in colour
- With an alkene, the bromine water changes from yellow/orange to colourless
- Ethene + Bromine -> diBromethane
Polymers
- Alkenes are known as monomers (single units). If we heat them and apply pressure, the double bond will break and a number of the alkenes monomers will add on to each other and make a polymer.
- Addition polymerisation involves the reaction of many unsaturated monomers to form a saturated polymer
- A hydrocarbon = A compound formed from carbon and hydrogen atoms only
- An unsaturated compound = Contains at least one double bond between its carbon atoms
- An addition polymer = is formed when alkenes react together and their double bonds are concerted to single bonds
- A covalent bond = is formed by sharing by sharing pairs of electrons
Designer polymers
- Polymer molecules in many plastics are attracted to each other only by a weak intermolecular force. These are easily overcome, so such plastics have low melting points. They are also easily stretched because the molecules can slide past each other
- Polymer molecules in other plastics have strong covalent bond between them. These cross links stop the molecules moving apart or ast one another. Such plastics have high melting points. They are rigid and cannot be stretched easily
Gore - Tex
- Made by laminating a thin film of plastic called expanded PTFE onto a layer of another fabric, such as a polyester or nylon. This makes the PTFE stronger
- The PTFE film has tiny holes which let water vapour through so it is breathable, but its waterproof since the holes aren't big enough to let big water droplets through and the PTFE repels water
Catalytic Converters
- The catalytic converter contains a catalyst made of platinum, rhodium and palladium. It is a solid alloy with lots of tiny holes or tubes that the carbon monoxide and nitrogen monoxide travel through before being emitted through the exhaust of the car. The gases land on the surface of the catalyst and because it is quite hot, they react together producing carbon dioxide and nitrogen - much less harmful gases
- Carbon monoxide + Nitrogen Monoxide -> Carbon Dioxide + Nitrogen
- Balanced equation : 2CO + 2NO -> 2CO2 + N2